In modern high-speed helical scan tape record/playback systems for use with magnetic or optical tape media in digital data recording applications, there is a need for transmission of wide bandwidth electrical signals between the rotating headwheel and the stationary portion of the recording/playback system. One method for electrically bridging the gap between the stationary and rotating assemblies involves the use of a slip-ring assembly, in which a conductive rotating ring is maintained in physical contact with a stationary brush. This method, however, is very susceptible to noise and, at the data rates in use by the systems contemplated, such noise as a slip-ring assembly generates may obliterate a significant amount of information.
A second method involves the transmission of light signals, modulated so as to convey information. Light signals provided by a laser, for example, may be directed axially onto the headwheel where a system of optics, e.g., mirrors, prisms, fiber optics, steer the beam onto a detector which converts the radiant energy to an electrical signal. This method is relatively complex and inefficient, and it requires extremely close tolerances in the alignment of the optical elements.
A third method, which is quite simple and relatively efficient, involves the use of inductive coupling across the gap between the rotating and stationary assemblies. A first winding in the stationary portion and a second winding in the rotating portion, when inductively coupled, comprise a rotary transformer. A driver circuit for use with a rotary transformer in a tape recording system is disclosed in U.S. Pat. No. 3,524,017, "Record Amplifier-Driver for Continuously Driving Analog Recorder Heads with an Optimum Record Current During the Life of the Head," issued Aug. 11, 1970, to E.I. Pezirtzoglou.
In high speed (5 to more than 20 Mbits per second) tape recording/playback systems in current use, data signals are transmitted between the stationary electronics and the rotating headwheel electronics at very high rates. Such signals are effectively passed through wideband transformers. Lower data rate systems (200 Kbits to 2 Mbits per second), however, strain the ability of a transformer to transmit the associated pulse widths faithfully, and, in particular, to transmit digital data streams containing a wide range of pulse widths. It is known that a transformer can effectively couple only ac signals, or dc pulses within a restricted range of pulse widths, between its windings. In order to use rotary transformers in applications where wide pulse widths must be accommodated, digital signals must be modulated in some fashion in order to pass over the gap and be detectable. Modulation of a digital signal necessarily entails further complexity and a reduction in the rate at which the data is communicated.
The present invention permits the transmission of digital information having a relatively wide bandwidth across a rotary mechanical gap while retaining the advantages of a rotary transformer.